Synthesis and characterization of palladium(II) complexes with new polydentate nitrogen ligands.: Dynamic behavior involving Pd-N bond rupture.: X-ray molecular structure of [{Pd(η3-C4H7)}2(Me-BPzTO)](4-MeC6H4SO3) [Me-BPzTO = 4,6-bis(4-methylpyrazol-1-yl)-1,3,5-triazin-2-olate]

The Ligands 2,4,6-tris(4-methylpyrazol-1-yl)-1,3,5-triazine (Me-TPzT), 2,4,6-tris(4-bromopyrazol-1-yl)-1,3,5-triazine (Br-TPzT), and 2-methoxy-4,6-bis(4-methylpyrazol-1-yl)-1,3,5-triazine (Me-BPzTOMe) have been synthesized and their reactions with some palladium derivatives explored. The palladium fragment [Pd(eta(3)-2-Me-C3H4)(S)(2)](+), S = acetone, reacts in acetone with Me-TPzT or Br-TPzT in a 3:1 molar ratio to generate new complexes in which two allylpalladium fragments are present and the TPzT ligands have been partially hydrolyzed: [{Pd(eta(3)-C4H7)}(2)(X-BPzTO)]A, X-BPzTO = 4,6-bis[4-methyl(or bromo)pyrazol-1-yl]-1,3,5-triazin-2-olate (X = Me, A = BF4, 1; A = PF6, 2; A = CF3SO3, 3; A = p-MeC6H4SO3, 4; X = Br, A = CF3SO3, 5). When the ligand Me-BPzTOMe is made to react with only 1 equiv of the palladium solvate, compound 6, [Pd(eta(3) -2-Me-C3H4)(Me-BPzTOMe)]CF3SO3, is isolated. Reaction of 6 with another 1 equiv of the palladium derivative leads to 3. The intermediate 7, [{Pd(eta(3)-2-Me-C3H4)}(2)(Me-BPzTOMe)]CF3SO3, has been isolated as an almost pure compound. The reaction of Me-BPzTOMe with 1 equiv of [Pd(C6F5)(2)(cod)] (cod = 1,5-cyclooctadiene) leads to the complex [Pd(C6F5)(2)(Me-BPzTOMe)], 8. Attention has been focused on the dynamic behavior, related with metallotropic phenomena, of the new complexes. H-1 NMR variable-temperature studies of complexes 1, 6, and 8 have been carried out. For 8, only one static species is observed, while, for 1 and 6, two isomers are detected at low temperature. Different Delta G(c)double dagger activation energies at the coalescence temperature have been determined and are ascribed to processes implying Pd-N bond ruptures. For 6, two different barriers are detected, corresponding to Pd-N(triazine) or Pd-N(pyrazole) bond ruptures. From the Delta G(c)double dagger data, it is concluded that the main driving force of the hydrolysis process is the formation of a better coordinating ligand. The molecular structure of 4 has been determined by X-ray diffraction. The meso isomer. in which the two C-Me axes of the allylic groups are oriented in the same direction, is found in the solid state.